Portable computers and other electronic devices continue to be reduced in size as advances in technology reduce the size of components used to manufacture these devices. Along with this size reduction, compact slots have been provided in the devices for receiving IC cards. In an effort to standardize IC card formats, the PCMCIA has promulgated various standards governing the physical dimensions and interface configurations of IC cards.
In brief, the PCMCIA standards set forth, among other things, IC card physical dimensions, electrical interface requirements between IC cards and the devices utilizing the IC cards, and a data format for the interchange of information between IC cards and devices utilizing IC cards. In addition to having 3 volt (130–150 mA) pins, PCMCIA slots (both standard size and “mini-PCMCIA” slots) also have two 5-volt pins, each of which source 500 mA, thereby limiting the sourcing capability of the 5-volt pins to a total of 1 A at 5 volts.
Computer manufacturers have endorsed the PCMCIA standards and have included at least one slot for a PCMCIA card in virtually all laptop, sub-notebook and notebook computers. In response to the increasing popularity of the PCMCIA standards, numerous PCMCIA-compatible devices, such as hard drives, modems, local area network adaptors and wireless communication systems have been developed. For example, one wireless communication card which serves the function of a wireless modem connectable to a cellular network is manufactured by Nokia under the product name D211. Sierra Wireless and others produce similar devices, referred to herein generically as “cellular IC cards”.
Cellular functionality can also be integrated into combination cards that combine wireless LAN (WiFi) and cellular capability. Given these integration capabilities, the computer user can plug a card into his/her PC or laptop that provides wireless/cellular capability. However, unlike many applications that use PCMCIA or similar slots, cellular hardware can have very high peak current and/or power requirements that can exceed the source capability of the PCMCIA slot for short periods of time. These peak current/power periods occur during transmit bursts, when the cellular power amplifier (PA) must transmit at power levels of over 2–3 W, worst case, and can/will draw more than the total of 1 A at 5 V available from the slot. This can be particularly problematic with new high data-rate standards, such as EDGE, which cause the PA to draw more current due to their low efficiency.
In an attempt to provide an on-demand temporary power source for use during these high-consumption periods, prior art systems have utilized a bank of large and expensive capacitors, requiring many capacitors in parallel, or one large super capacitor cell. However, the use of the capacitors is not without its drawbacks. For example, capacitors can be relatively expensive, have high leakage currents, and consume a significant amount of space on the PC board of the card, both on the board surface and in terms of height.